1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus and an auto color registration method thereof, and more particularly, to an image forming apparatus improved in auto color registration and an auto color registration method thereof.
2. Description of the Related Art
An image forming apparatus (such as a printer, a multi-function peripheral, a scanner, etc.) that forms a color image includes laser scanning units (LSU) provided to correspond to a plurality of colors, and an image forming unit provided with a plurality of photosensitive bodies or the like. The plurality of photosensitive bodies or the like are arranged along a transport path for a print medium transported by a transport unit, such as a transport belt.
In the image forming apparatus, to precisely print a color image on a print medium, positions where image transfers to the print medium start are to correspond with each other for the plurality of colors. Similarly, positions where image transfers to the print medium end are to correspond with each other for the plurality of colors. To this end, the image forming apparatus performs an auto color registration (ACR). The ACR is implemented to inspect whether the images corresponding to colors are correctly registered on the transport belt and printed, and to automatically correct if there is mis-registration.
In detail, the image forming apparatus detects a plurality of patterns corresponding to a plurality of colors transferred onto the transport belt, and applies the ACR to a color shifted out of position. Specifically, the image forming apparatus measures an X offset and a Y offset according to a difference in a space between the plurality of detected patterns, and performs the ACR using the measured X and Y offsets so that the plurality of patterns corresponding to the plurality of colors are registered in position.
However, the ACR is based on the difference in a space between the patterns detected by an optical scanning unit. As a result, differences in light quantity according to colors can cause a detected value of the pattern width to differ from the real pattern width. For example, K (Black) absorbs more light than those of other colors, and thus a pattern width of K (Black) may be detected as larger than those of C (Cyan), M (Magenta) and Y (Yellow), even though their pattern widths are the same.
To reduce the difference in the detected pattern width, there has been conventionally proposed a method of increasing the light quantity for detection or transferring a large pattern width. However, the above method still has a problem due to the difference in the detected pattern width among colors, so that a correction effect is low and power and/or developers may be wastefully consumed. Thus, the difference in the detected pattern width between colors may cause an error in space difference between the patterns for the ACR, thereby lowering the reliability of the ACR.